Table 3 Basic techniques used for the characterization of magnetic nanoparticles
From: Pharmacokinetics of magnetic iron oxide nanoparticles for medical applications
Technique | Advantages | Drawbacks | Refs. |
|---|---|---|---|
Imaging techniques | |||
Transmission Electron Microscopy (TEM) | - Detection of nanoparticles distributed in intracellular and extracellular thin fragments of tissues - Differentiation nanoparticles located in different structures - Information on biodistribution and MNPs degradation ways in the organism | - Costly preparation procedures - Information only from specific, very limited areas of tissue | |
Magnetic Resonance Imaging (MRI) | - Noninvasive and repeatable method - Visualizing and distinguishing individual soft tissue - Used in examinations of practically the entire body - Possibility of continuous imaging of moving objects in real time | - Necessity of application a very strong magnetic field - Quite expensive technique | |
Magnetic Particle Imaging (MPI) | - Prominent contrast and signal-to-noise ratio - The selected region can be rapidly and continuously detected for real-time imaging of MNPs distribution | - Necessity to develop and apply the appropriate MPI tracers | |
Spectroscopy techniques | |||
Electron Spin Resonance (ESR) | - Characterization of physical properties of various nanomaterials - Observation the differences resulting from interaction between the material surface and environment - Differentiation between the endogenous and administered iron | - Results for only specific time points - The necessity to section the tissue samples in to 2 mm3 cubes to fit in the thin ESR glass tubes | |
Inductively Coupled Plasma (ICP) techniques coupled with Atomic Emission Spectroscopy (ICP-AES) or with Mass Spectroscopy (ICP-MS) | - Detection of iron present in tissues at very low concentrations | - Destructive methods - No differentiation between the endogenous and administered iron | |
Electron Paramagnetic Resonance (EPR) | - Sensitive and nondestructive method which results in a direct measurement of the MNPs not requiring further data analysis - Performed at low magnetic fields and frequencies, offering the advantage that a much larger sample volume can measured at room temperature - EPR can be combined with MRI which benefits among others in cell tracking studies | - Limitations of the method result from the instability of paramagnetic centers in the tested substances and the reduced sensitivity of their detection for samples containing water | |
Ferromagnetic Resonance Spectroscopy (FRS) | - Powerful method for the quantitative determination of internal fields in ferro- or ferrimagnetic materials and nanostructures - Shape of the FMR spectrum contains valuable information about the internal fields in the sample | - Structural information cannot be obtained in a straight-forward way from spectra | [192] |
Alternating Current (AC) Susceptibility (ACS) | - Non-invasive method - Tissue sample preparation is minimal and no separation or isolation procedures are needed for the simultaneous quantification of several iron-containing species - The large amounts of tissue can be characterized each time so that representative results are easily obtained | - The need to use ex vivo samples - Time, costs and the relatively low availability of these type of instruments | |
Magnetometry techniques | |||
Magnetic Susceptibility Measurement (MSM) | - A fast and easy method to quantify MNPs in convenient and accurate way in different media - There is no need of any preliminary modification of the samples - MSM values are only influenced by the iron from magnetic particles and not by free iron in solution | - The same magnetic particles for the calibration and experiments must be used, magnetic susceptibility being sensitive to the size of the magnetic core | [25] |
Technique with the use of Superconducting Quantum Interference Device (SQUID) | - Very sensitive technique - These instruments are used in MRI and magnetoencephalography (MEG) for recording the very weak fields, which are produced by electrical currents flowing in the brain’s neural networks | - The noise level is determined by environmental sources, except in those experiments where the SQUID and its signal source are enclosed in a superconducting shield | [193] |
Magnetic Particle Quantification (MPQ) | - Method offers highly sensitive, room-temperature and rapid quantification of nanoparticle–cell interactions - The low invasiveness and high resolution - Possibility of measuring very low amounts of the nanoparticles without destruction of sample - Llow amplitude and frequencies used in MPQ protect the MNPs from heating and agglomeration | - Necessity to use only MNPs with nonlinear magnetization - MPQ method cannot distinguish the processes of particle dissolution, transformation of iron oxides to biological forms of iron, excretion of particles from the organism, etc. | |